# Climate Change: Assignment – Using an Empirical Climate Model

This assignment makes use of an empirical climate model produced by Colorado College.

Last week you had a chance to explore a Global Climate Model (EzGCM). Dr. Schmidt describes these models as “the physics-based, three-dimensional, coupled atmosphere-ocean climate models”.  These models account for different factors (C02 concentrations, temperatures, etc.) and use our knowledge of physics to calculate interactions of the oceans and atmosphere in order to estimate climate change.

Instead of physical equations, empirical models use historical observations of climate variables and compare them to observed climate forcings. For example, such a model can correlate past concentrations of atmospheric CO2 to past temperature records, establishing a mathematical relationship between the two. Although correlations do not necessarily imply cause and effect, they do provide us with a degree of predictive capability as well as insights into potential physical linkages in the climate system.

Open the model as you read the description below: Empirical Climate Model

The model explores four variables – El Nino, volcanic eruptions, solar irradiance, and human-caused (anthropogenic) greenhouse gasses – to examine the effect each has on global temperature. Take a look at the model. You will see two graphs.

The top graph (Temperature Records 1980-2018) shows observed fluctuations in temperature (anomalies) in black. This is data collected using weather stations and satellites. The green line is the line of best fit. It is the closest that these four variables come to correlating to the observed data (the black line). The red line reflects the changes you make in the four variables. Notice that it changes as you move the sliders below the graph. The red vertical bar to the right of this graph shows you the amount of data these four variables explain. When all the variables are set to “1” (the best fit) the bar reads 0.839. This means that 83.9% of the observed data are explained by the settings of the four variables. As you move the sliders this value will change.

The lower graph (Climate Forcing Components, 1980-2018) shows the individual contribution of each variable to the red line in the top graph based on how you have the sliders set. Note that the values on the y-axis (Temperature anomaly) are different on both graphs.

Start by looking at the individual contribution of each variable by moving all the sliders except one to zero. Record the results in the table below and repeat this procedure for the other three variables. Observe the way that the red line in the top graph reflects changes that you make in the settings.

Try different settings for the variables and see how they change the model. Observe how the different variables interact. (An interesting combination is to set Anthropogenic and Solar Cycles to zero and look at the way the effects of Volcanoes and El Nino have interacted.)

Observations and Reflection

1. Describe some of the settings you experimented with and analyze the results.
1. What conclusions about the overall effects of these four variables on observed temperature fluctuations can you make based on this model?
1. What is the difference between an empirical model like this one and a Global Climate Model (like EdGCM)? What do you think are the strengths and weaknesses of each type of model?
1. How do you think climate scientists use empirical models?

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